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Copy 3 FM 21-26
WAR DEPARTMENT
BASIC FIELD MANUAL
Jfr
ADVANCED MAP AND AERIAL
PHOTOGRAPH READING
September 17,1941
FM 21-26
BASIC FIELD MANUAL
ADVANCED MAP AND AERIAL
PHOTOGRAPH READING
Prepared under direction of the
Chief of Engineers
UNITED STATES
GOVERNMENT PRINTING OFFICE
WASHINGTON : 1941
For sale by the Superintendent of Documents, Washington, D. C.
WAR DEPARTMENT,
WASHINGTON, September 17, 1941.
PM 21-26, Advanced Map and Aerial Photograph Reading,
is published for the information and guidance of all con
cerned.
[A. G. (5-15-41).]
BY ORDER OP THE SECRETARY OF WAR:
G. C. MARSHALL,
Chief of Staff.
OFFICIAL:
E. S. ADAMS,
Major General,
The Adjutant General.
DISTRIBUTION:
D (3); B 1, 2, 4, 6, 7,17 (2); R 1-7,10, 17 (5); Bn 1 (10),
2-7, 11, 17 (5), 9, 10 (2); C 2, 5-7, 17 (10), 1, 3, 4.
9-11 (5).
(For explanation of symbols see PM 21-6.)
ii
TABLE OP CONTENTS
Paragraphs Page
SECTION I. General ________i—____————— 1-9 1
II. Distance ________1________—— 10-15 10
IH. Direction, orientation, and location.——— 16-28 20
IV. Coordinates ____________————— 29-38 41
V. Elevation and relief————_———... 39-48 61
VI. Slope, profile, and visibility_____—_ 49-60 73
VH. Aerial photographs______——._——___ 61-75 87
Vin. Identification of terrain features on sin
gle photograph———————————————— 76-88 113
IX. Stereovision and examination______. 89-93 129
X. Preparation of aerial photographs for use
as map substitute_________— 94-114 148
XI. Photomaps ____________________ 115-120 175
INDEX „———_______..-——————————__ 183
FM 21-26
BASIC FIELD MANUAL
ADVANCED MAP AND AEKIAL PHOTOGBAPH
BEADING
(Tbis manual'supersedes TM 2180-5, September 28, 1938.)
SECTION I
GENERAL
• 1. PURPOSE.—The purpose of this manual is to provide
a text on map and aerial photograph reading for training
of military personnel already familiar with basic elements
covered b